Sorry for later reply, you simply copy the API code from the page as below and then embed it into your website, it will be displayed. Generally speaking, you cannot see the result in preview.
I can’t say that I’m an expert in it, but I’m always interested in learning something new, so I recently read about API and integration. I can advise you to read the information on this resource https://api2cart.com/api-technology/api-integration-definition-and-meaning/ , and also on this site you can just find a great and reliable API2Cart interface for API integration